1. Field of the Invention
The present invention relates to an optical connector for connecting optical fibers, particularly to a ferrule for holding a tip of the optical fiber.
2. Background Information
In coherent optical fiber communication and in optical interference measurement such as that using an optical fiber gyroscope, or in similar applications, a polarization maintaining optical fiber capable of transmitting light while maintaining the orientation of the plane of polarization of the transmission light has widely conventionally been used.
To connect an end of this polarization maintaining optical fiber to an end of another polarization maintaining optical fiber, or to other optical elements, the connection has to be made in a manner that can provide a high extinction ratio transmission. Therefore adjustment has to be made, before the connection, on the angle of the plane of polarization of the polarization maintaining optical fiber, i.e., the angle of rotation about the axis of the optical fiber.
A ferrule into which the polarization maintaining optical fiber is inserted to be held is usually composed of a ferrule tubular body and a collar member. The ferrule tubular body is formed of hard ceramic such as zirconia, or glass or like other materials and has an optical fiber insertion hole. The collar member is provided at the rear end of the ferrule tubular body, and has a coated optical fiber insertion hole that is communicated with the rear end of the optical fiber insertion hole to hold the coated optical fiber. Metals such as stainless steel, plastics, ceramics or the like can be used to form the collar member. The optical fiber insertion hole provided inside the ferrule tubular body receives the optical fiber, namely, the coated optical fiber with its coat removed at the tip, and the optical fiber inserted therein is bonded to the ferrule with an adhesive or the like.
When the optical fiber is bonded to the ferrule, the bonding has to be made only after the orientation of the plane of polarization of the optical fiber is aligned with the position of a ferrule positioning groove with an allowance of xc2x13xc2x0. For that reason, a microscope is used to observe the facet of the optical fiber and adjust the angle of rotation about the axis of the optical fiber, so that the optical fiber can be bonded and fixed to the ferrule tubular body at the appropriate position. The adjustment operation, however, is problematic because it is difficult, lacks precision and takes time.
A ferrule has been proposed in order to eliminate such inconveniences. In this ferrule, its collar member is composed of two separate members. One is a cylindrical holder and the other is an annular collar member which is formed along the outer periphery of the holder and which has a concave portion serving as a positioning key in a housing.
According to this ferrule, an optical fiber is bonded and fixed to a ferrule tubular body to which the holder is fitted and the end face of the ferrule tubular body is polished. The polished end face of the ferrule tubular body (facet of the optical fiber) is observed through a microscope to adjust the angle of rotation about the axis of the optical fiber, and then the collar member is bonded and fixed to the outer peripheral surface of the holder. The orientation of the plane of polarization of the optical fiber thus can be aligned.
Unfortunately, the angle of rotation of the ferrule tubular body is easily shifted as well as the end face thereof in the radial direction when the collar member is to be bonded at an appropriate position while adjusting the orientation of the plane of polarization of the optical fiber.
Moreover, assembly of the proposed ferrule is time consuming because it requires time for an adhesive to cure if the annular cover member is bonded to the holder using the adhesive.
An object of the present invention is therefore to provide a ferrule and an optical connector in which assembly can easily be made with high precision in a shortened period of time.
The present invention overcomes the drawbacks of the conventional art. In a first aspect, the present invention is directed to a ferrule. In a first embodiment, the ferrule comprises:
a ferrule tubular body for holding an end of an optical fiber;
a holder provided at the rear end of the ferrule tubular body in order to hold a coated optical fiber; and
a collar member having a through hole through which the holder can be inserted and, on its outer peripheral surface, a positioning groove for positioning with respect to an optical connector housing, the collar member being welded to or fused with the holder.
In a second embodiment, the holder and the collar member are formed of a metal, and the outer peripheral surface of the holder and the inner peripheral surface of the collar member are fixed to each other by welding.
In a third embodiment, the holder and the collar member are formed of a metal, the holder has a flange portion protruding along the outer peripheral surface thereof like a disc, and the flange portion is fixed to the peripheral edge of the collar member by welding.
In a fourth embodiment, the outer peripheral surface of the collar member and the outer peripheral surface of the holder are fixed to each other by welding.
In a fifth embodiment, the holder has a large diameter cylindrical portion to be fitted to the ferrule tubular body, the flange portion is placed at substantially the center of the large diameter cylindrical portion in the axial direction of the holder, and
the collar member is fixed to the flange portion on the ferrule tubular body side.
In a sixth embodiment, the flange portion is placed along the outer periphery of an end of the holder on the ferrule tubular body side, and
the collar member is fixed to the flange portion on the side opposite to the ferrule tubular body.
In a seventh embodiment, the holder and the collar member are formed of a resin,
the holder has a first tapered portion whose outer diameter is gradually reduced toward its rear end,
the through hole of the collar member has a second tapered portion whose inner diameter is gradually increased toward the opening into which the holder is inserted, and
the holder and the collar member are fixed to each other by deposition between the first tapered portion and the second tapered portion.
In an eighth embodiment, the optical fiber comprises a polarization maintaining optical fiber.
In another aspect, the present invention is directed to an optical connector utilizing the ferrule according to any one of the first to eighth embodiments of the invention.
In another aspect, the present invention is directed to a method of manufacturing a ferrule, comprising the steps of:
fitting a holder for holding a coated optical fiber to the rear end of a ferrule tubular body for holding an end of an optical fiber; and
welding to or fusing with the holding unit a collar member having a through hole through which the holder can be inserted, the collar member also having on its outer peripheral surface a positioning groove for positioning with respect to an optical connector housing.
In a first embodiment of the method of manufacturing a ferrule according to the invention, the holder and the collar member are formed of a metal, and the outer peripheral surface of the holder and the inner peripheral surface of the collar member are fixed to each other by welding.
In a second embodiment of the method of manufacturing a ferrule according to the invention, the holder and the collar member are formed of a metal,
the holder has a flange portion protruding along the outer peripheral surface thereof like a disc, and the flange portion is fixed to the peripheral edge of the collar member by welding.
In a third embodiment of the method of manufacturing a ferrule according to the invention, the outer peripheral surface of the collar member and the outer peripheral surface of the holder are welded to each other.
In a fourth embodiment of the method of manufacturing a ferrule according to the invention, the holder have a large diameter cylindrical portion to be fitted to the ferrule tubular body, the flange portion is placed at substantially the center of the large diameter cylindrical portion in the axial direction of the holder, and
the flange portion is inserted through the collar member from the ferrule tubular body side of the flange portion and is welded to the collar member.
In a fifth embodiment of the method of manufacturing a ferrule according to the invention, the flange portion is placed along the outer periphery of an end of the holder on the ferrule tubular body side, and
the flange portion is inserted through the collar member from the side opposite to the ferrule tubular body and is welded to the collar member.
In a sixth embodiment of the method of manufacturing a ferrule according to the invention,
the holder and the collar member are formed of a resin,
the holder has a first tapered portion whose outer diameter is gradually reduced toward its rear end,
the through hole of the collar member has a second tapered portion whose inner diameter is gradually increased toward the opening into which the holder is inserted, and
the holder and the collar member are fixed to each other by fusion between the first tapered portion and the second tapered portion.
In a seventh embodiment, a method of assembling an optical fiber comprises the steps of:
fitting a holder having a flange on its outer periphery to the rear end of a ferrule tubular body;
bonding and fixing an optical fiber thereto;
polishing an end face of the ferrule tubular body;
observing the ferrule tubular body through a microscope to adjust the angle of rotation about the axis of the optical fiber; and
welding to or fusing with the flange a collar member that has a positioning groove.
In an eighth embodiment, in the method of assembling an optical fiber according to the seventh embodiment of the invention the adjustment of the angle of rotation is made by transmitting light through the optical fiber.
In a ninth embodiment, in the method of assembling an optical fiber according to the seventh embodiment of the invention, the optical fiber is a polarization maintaining optical fiber.
In a tenth embodiment, in the method of assembling an optical fiber according to the ninth embodiment of the invention, the adjustment of the angle of rotation is made based on the position of a core of the polarization maintaining optical fiber and the position of stress imparting portions.
In an eleventh embodiment, in the method of assembling an optical fiber according to the tenth embodiment of the invention, the position of the core of the polarization maintaining optical fiber and the position of the stress imparting portions are obtained from a plurality of straight lines each of which is tangential to the stress imparting portions and intersects with the rest of the lines in the view field of the microscope, and from the position of the center of the core.
In a twelfth embodiment, in the method of assembling an optical fiber according to the tenth embodiment of the invention, the position of the core of the polarization maintaining optical fiber and the position of the stress imparting portions are obtained from a plurality of parabolas each of which is tangential to the stress imparting portions and intersects with the rest of the parabolas in the view field of the microscope, and from the position of the center of the core.
In a thirteenth embodiment, in the method of assembling an optical fiber according to the tenth embodiment of the invention, the position of the core of the polarization maintaining optical fiber and the position of the stress imparting portions are obtained from a plurality of hyperbolas each of which is tangential to the stress imparting portions and intersects with the rest of the hyperbolas in the view field of the microscope, and from the position of the center of the core.
In a fourteenth embodiment, in the method of assembling an optical fiber according to the seventh embodiment of the invention, the microscope is at least one microscope selected from the group consisting of a phase contrast microscope, a differential interference microscope, a laser microscope, and a scanning tunneling microscope.
In a fifteenth embodiment, in the method of assembling an optical fiber according to the ninth embodiment of the invention, the angle of rotation is adjusted based on image recognition of the image observed through the microscope and based on adjustment of the relative position of an angle formed by the collar member and a support portion.
In a sixteenth embodiment, a method of assembling an optical fiber comprises the steps of:
fitting a holder having a flange on its outer periphery to the rear end of a ferrule tubular body;
bonding and fixing an optical fiber thereto;
polishing an end face of the ferrule tubular body;
adjusting the angle of rotation about the axis of the optical fiber such that the maximum extinction ratio can be obtained; and
welding to or fusing with the flange a collar member that has a positioning groove.
In a seventeenth embodiment, a method of assembling an optical fiber comprises the steps of:
fitting a holder having a flange on its outer periphery to the rear end of a ferrule tubular body;
bonding and fixing a polarization maintaining optical fiber thereto;
polishing an end face of the ferrule tubular body;
disposing a collar member in a light source through a polarizer;
arranging, through an analyzer, an optical power meter in an end of the optical fiber which is not provided with the ferrule tubular body;
adjusting the angle of rotation of the optical fiber about the axis of the optical fiber based on the output of the optical power meter; and
welding to or fusing with the flange the collar member that has a positioning groove.
In an eighteenth embodiment, the method of assembling an optical fiber according to the seventeenth embodiment of the invention, further comprises a step of rotating the analyzer to obtain the extinction ratio and adjust the angle.
According to the present invention, the holder and the collar member are fixed to each other by welding or fusion. This makes it possible to facilitate the adjustment of the position of the plane of polarization of the optical fiber held by the ferrule tubular body with respect to the position of the groove of the collar member, as well as to shorten the time required for the assembly.